Mold Making Rhino

Hey Kyle,

No matter how hard i am trying to hold myself asking you the way on how to achieve the splitting on these parts, i couldn’t do it. :expressionless:

:disguised_face: So how did you used you do this?
Is it attainable within Rhino, or does this involves other softwares?

Fun Fact,
I can do the mold as Mesh and it looks preety neat, but then (there is always one then) the file gets too “heavy” in terms of data, and the CAM softwares are strugling in handling the files.
If i would decimate the mesh file, i am getting poor result in terms of detail quality.

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Hey Mate,

I can understand that among others you have also put a considerable amount of time on similar process.
Can you please explain, when and why does a trim fails, based on a parting line? That could help huge!

That’s because you are using techniques the will only work in simple geometry.

There is a lot in your model that is designed to fail:

Making the parting as you have is problematic. In some spots using the ribbon command to make the parting makes a degenerate surface and that is pretty much guaranteed to cause any trimming joining or booleans to fail. Also using subD to create surfaces has resulted in numerous places where vertices land very close (less than tolerance) to the parting that is another almost guaranteed fail when it come to trimming and joining the part to the parting.

I fixed about a dozen places where the above problems were found by either modifying the parting or modifying the part where it crosses the parting. Also I extended the parting surfaces a little so that they fully intersect the part.
mold1.3dm (14.0 MB)

This is the result after trimming and joining the model and parting.
Inciderntly the trimming and joining works much better and faster in Rhino6 than it does in Rhino8.
mold2.3dm (15.2 MB)

If I were doing this the first thing I would do is come up with a better smoother parting surface. Before doing anything else. Then when you fixed up the geometry to eliminate undercuts you would do that with respect to the parting. A simpler parting would be easier to point edit if you need to change it a little while fixing the geometry.

There is no decent automated process to making a complicated parting surface. Even the expensive CAD software with dedicated mold making tools will make a messy parting on something like this.

Also if this is going to be CNC machined you should try to make a parting surface that has radius of curvature that is larger than the tooling that is going to cut the mold if you want the mold to close properly.


@jim 's advices are the best!
And, as I said too, you have to manually adjust your parting line so it lands on a proper place on the part. Also, for the trimming, you should extract the surfaces that you want to trim from the part, trimming them one-by-one. You’ll see where are the problems.


The model being a composition of 1,986 surfaces, does in fact bring forth a bit of extra complexity.

You just need a nice clean parting line is all. The ribbon you have already just needs some TLC, and it should work fine.

The mesh format is merely just another type of composition. The game there would be how you manage that particular format composition is all. Rhino doesn’t have the easiest mesh tools, but it’s certainly improving big time with R7 and now R8.

By the time R10 comes out, there’ll prob be some super coo mesh tools :sweat_smile: Maybe even voxels! :smiley:

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:neutral_face: It’s all good, man!

Jim, your work is seriously blowing my mind! You’re spot-on about my Rhino skills—definitely in noob territory. I’m curious, how do you even spot these issues in the first place (Intersect, right?), and what’s the secret sauce for fixing them?

The cool thing is, it’s doable. Your insights got me excited to dig deeper into Rhino. I’ve already leveled up thanks to your and everyone else’s guidance. Much appreciated for the time you’ve put into this!

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I attached a tribute I threw together as demonstration. I did skip a few steps and didn’t really finish, but was short on time. I hope it helps show some proof in the pudding.

HeadF_SubD_FUSolid_Undercutremv_HalfMoldReady_emod.3dm (18.1 MB)

I kinda butchered the speed because of the 20MB limit. :expressionless:

Indeed. This is where design intent comes into play. While I see alot of power in the draft analysis and the transparency ability, while using the gumball to manipulate the cutting geometry etc.

Basically, think of the parting line as the intersection of a 3D-cutting-blade that must encapsulate your entire geometry in order to do a full split in one instance.

If the blade doesn’t cut the whole thing apart at one instance, it just wont work.

The ‘blade’ has to be completely, concisely, and cleanly created 100% in order to work.

The file tolerance probably has some impact on weather it’s 100% or 99.9%, but the ‘cutting’ geometry has to be setup cleanly or the split will fail.

You also have to make sure the cutting geometry isn’t intersecting multiple times through the part needlessly.

It’s upto the designer to decide these things, of course, while bystanders like myself can only assume.

For any given phenomena there’s infinitely many interpretations.

You can see a few areas that I probably skipped some steps in a symmetrical sense or lack thereof:

I basically refined a few areas but skipped the other side :relieved:

But the basic idea here, that is being discussed is, the science behind the ‘blade’ that cuts the parting-line. That’s where the attention should be, and it could very well take weeks of work to get it perfect. It all depends on design intent etc.

At least we know it works, which helps condone the potential addition of time needed for refinements.

Here’s that part again at a lil bit slower speed :joy::

I really like that workflow of, being able to see the part transparently (using locked object transparency) while draft analysis is active, and using the gumball to adjust the surface that will split the part, thereby fine-tuning the partingline while seeing the draft constrast – omg so awesome, Rhino so awesome. :smiley:

Now we just need the draft analysis to automatically make the ribbon all the way around :smiley:


for the miniatures I was doing I had to explode the model with it’s thousands of individual surfaces (they were autowrapped from freeform) and split each face one at a time (or a few at a time) with the parting line. once they were split, I joined them back up and checked for naked edges with showedges.

tedious work, but I was charging by the hour.

I was told once by a mentor- “sometimes, the only way to do the work is to do the work…”

made for beautiful molds tho…

this is the group I was working for-

crazy detailed stuff. the machinist I was working with was an artist/ mad genius and did these on a high speed mill . The molds were mirror finished when they came off the machine.